[PATCH] Bluetooth: Avoid use of session socket after the session gets freed

[Dean_Jenkins@mentor.com]

From: Vitaly Kuzmichev <vitaly_kuzmichev@mentor.com>

The commits 08c30aca9e698faddebd34f81e1196295f9dc063 "Bluetooth: Remove
RFCOMM session refcnt" and 8ff52f7d04d9cc31f1e81dcf9a2ba6335ed34905
"Bluetooth: Return RFCOMM session ptrs to avoid freed session"
allow rfcomm_recv_ua and rfcomm_session_close to delete the session
(and free the corresponding socket) and propagate NULL session pointer
to the upper callers.

Additional fix is required to terminate the loop in rfcomm_process_rx
function to avoid use of freed 'sk' memory.

The issue is only reproducible with kernel option CONFIG_PAGE_POISONING
enabled making freed memory being changed and filled up with fixed char
value used to unmask use-after-free issues.

Signed-off-by: Vitaly Kuzmichev <Vitaly_Kuzmichev@mentor.com>
Acked-by: Dean Jenkins <Dean_Jenkins@mentor.com>
---
 net/bluetooth/rfcomm/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index facd8a7..5632146 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -1857,7 +1857,7 @@ static struct rfcomm_session *rfcomm_process_rx(struct rfcomm_session *s)
 	BT_DBG("session %p state %ld qlen %d", s, s->state, skb_queue_len(&sk->sk_receive_queue));
 
 	/* Get data directly from socket receive queue without copying it. */
-	while ((skb = skb_dequeue(&sk->sk_receive_queue))) {
+	while (s && (skb = skb_dequeue(&sk->sk_receive_queue))) {
 		skb_orphan(skb);
 		if (!skb_linearize(skb))
 			s = rfcomm_recv_frame(s, skb);
-- 
1.8.1.5